In battle, my paladin holds his holy symbol aloft and cries out in a thunderous voice, "In the name of Nathan Silverhome I call thee! Dius! Come to my side! Evil stands before us, and our battle begins anew!" A beam of light fires from the Sunmask of Pelor, opening up a shining argent portal to Mount Celestia, and my pally's mount comes thundering through, ready to do battle at his companion's side once again.
I had a similar idea, though without the "By the Power of Greyskull" part, but for Ravenloft. In Raveloft, when the Paladin summons his mount, a deep mist would suddenly blow in around the Paladin, and out of this deep mist would appear the mount as if it'd always been there.
Well, I like to think that my image isn't quite so cartoony as He-Man. At least, that's what I like to tell myself.
Have you ever thought of taking a Dire Tiger mount? If so, I suggest naming it Battle-Cat.
Nothing midstream about it. Characters are created at level 1. You don't have to discuss a level 5 ability until you are level 5.
Most games end long before characters gain four levels.
It is midstream, because a player who creates a character at Level 1 expecting his character to develop a certain way is going to be pissed if the DM doesn't tell him until Level 5 that his character, in fact, will be developing in a completely DIFFERENT way then he thought it would. Really, if you're a DM, and you're going to make a House Rule altering one or more abilities of a player class, how much trouble would it be to, oh, I don't know, TELL THE PLAYER BEFORE HE MAKES THE CHARACTER? God forbid that the player be fully informed when making his choice.
Even if the campaign doesn't make it to 3rd-Level, is telling the player beforehand REALLY such an onerous thing to expect of the DM? Whereas it's a big deal for the player, because he might not want to play that class from Level 1 if he doesn't like the DM's changes. Yeah, he could always make a new Level 5 character to replace his old one which has suddenly lost its appeal, but you, as the DM, have just taken a big old dump on the player. You've left him with only two options. A) Continue with a character that's been changed in such a way that he might not like, which'll reduce the enjoyment of the game for him, or B) Throw away every bit of development he's invested into that character up til that point in favor of a brand new character which he's going to have to start working on from scratch (And I don't mean level and equipment wise. Playing a 10th-level character isn't the same as playing a character from 1st-level to 10th-level). He may not mind the changes, if you're lucky, but once again, IS it so much trouble to let the player know BEFOREHAND of the changes? So may not be bothered, but some may be pissed off greatly.
Point is, if you've got any house rules which would affect the players choice of which character to play, then it's your responsibility to tell the players the house rules BEFORE the campaign starts. You shouldn't wait until they've worked hard to advance their character to a certain level in order to get a certain power, only to tell them at that point that the power they've been looking forward to won't work anything remotely like how they were expecting.